The oil, gas and petrochemical industry desires to efficiently obtain hydrocarbons and process the hydrocarbons to produce desired products. Refining processes involve upgrading, converting or separating hydrocarbons (e.g., crude oil) into different streams, such as gases, light naphtha, heavy naphtha, kerosene, diesel, atmospheric gas oil, asphalt, petroleum coke and heavy hydrocarbons or fuel oil. Similarly, natural gas may be converted into industrial fuel gas, liquefied natural gas (LNG), ethane, propane, liquefied petroleum gas (LPG), and natural gas liquids (NGLs). The oil and gas processes are also often integrated with petrochemical systems to convert refinery streams into chemical products such as ethylene, propylene or polyolefins.
To convert hydrocarbon feeds into petrochemical or basic chemicals, chemical conversion processes may be utilized. These processes typically involve using thermal or catalytic reactors or furnaces to produce reactive hydrocarbon products, such as acetylene, ethylene or propylene in different proportions. As an example, steam cracking reactors are commonly utilized to convert the hydrocarbon feed into ethylene and acetylene, which may be further processed into various chemical products. The steam cracking reactors are utilized because they provide feed flexibility by being able to utilize gas (e.g., ethane) and liquid (e.g., naphtha) feeds. However, these feeds due to their high hydrogen content do not typically require hydrogen to manage reactor products from the process.
Historically, the oil and gas refineries utilize the higher value distillates from the hydrocarbon feed, which are typically fungible fuels, such as mogas, natural gas and diesel. As a result, the petrochemical refineries utilize the remaining fractions, such as ethane, propane, naphtha and virgin gas oil, in their processes. However, few chemical conversion processes are able to directly employ natural gas or the lower value refinery feeds, such as aromatic gas oils or fuel oils. As such, there is a need for a process that can produce ethylene and acetylene from different feeds, such as advantaged feeds (e.g., natural gas and/or aromatic gas oils, for example).
To process these feeds, high-severity conditions (e.g., more severe operating conditions, such as higher temperatures) are generally involved to produce products having a higher value than the feed. High-severity conditions enable methane cracking and aromatic ring cracking, which do not occur at appreciable rates at typical low-severity conditions (e.g., conventional steam cracking conditions). At high-severity conditions, the primary products of thermal chemical conversion processes are acetylene and ethylene along with hydrogen (H2) and coke, which may vary in proportion depending on the temperatures, pressures, residence times and feed type utilized in the conversion process. Low-severity conditions may be still be used to convert higher hydrogen content refinery byproduct streams. At lower severity conditions, saturates may be converted to ethylene, propylene and butenes and alkyl aromatics may be converted to benzene, toluene and gasoline blend stock. Although high-severity operating conditions typically yield predominately acetylenes along with hydrogen, acetylene may be further hydrogenated to ethylene and ultimately polyethylene or other derivatives using conventional technology.
High-severity and low-severity conversion processes are typically based on different pyrolysis reactors, which may include pyrolysis alone or integrated with combustion chemistry. That is, the reactors may include pyrolysis chemistry (e.g., thermochemical decomposition of feed at elevated temperatures in the absence of oxygen) alone or in combination with combustion chemistry (i.e., exothermic chemical reactions between a fuel and an oxidant). These pyrolysis reactors can be divided into different types: partial combustion that burns part of the pyrolysis feed, indirect combustion that involves contacting the pyrolysis feed with combustion products, arc process that generate the electric arc or plasma to crack the pyrolysis feed, and thermal pyrolysis. Each of these pyrolysis types differs in the means of generating and transferring the heat for the pyrolysis, but can be broadly characterized as low-severity or high-severity.
Low-severity thermal processes, such as steam cracking or the Wulff process, are unable to significantly convert methane, which is a hydrogen rich hydrocarbon that yields excess hydrogen when cracked. Likewise, low-severity processes are unable to react severely hydrogen deficient feeds, such as aromatic rings, that require excess hydrogen or hydrogen rich feeds as a co-reactant. These processes feed higher hydrogen feeds that may crack at lower temperatures (e.g., ethane or naphtha), which favors high ethylene yields (e.g., acetylene yields are typically less than (<) 2 wt % of the reactor product).
Due to the low acetylene concentrations with low-severity processes and high ethylene concentrations, the reactor products may be managed without concern for acetylene autodecomposition. Typically, for low-severity operating conditions, the levels of acetylene are relatively low as compared to the ethylene concentrations produced, while high-severity operating conditions produce lower concentrations of ethylene and higher concentrations of acetylene. Accordingly, for high-severity processes, acetylene manufacture may involve special handling procedures if the acetylene concentrations above certain thresholds. That is, acetylene may be handled properly at low pressure and at low concentrations, but may be problematic at higher pressures and higher concentrations. Accordingly, special handling procedures and considerations are considered if operating with concentrated acetylene at elevated pressures to avoid autodecomposition or detonation.
Further, the acetylene concentrations are typically managed through different techniques. For instance, acetylene manufacturing plants absorb a raw acetylene stream into a polar liquid, such as dimethyl formamide (DMF), acetone, N-methyl pyrollidone (NMP) or methanol, to separate the acetylene from light gases. As an example, U.S. Pat. No. 7,208,647 describes using dilute absorbed acetylene by converting the liquid acetylene mixture to ethylene via an improved liquid phase hydrogenation process. Therefore, the reference avoids acetylene concentration at pressure, but has to remove substantially all the hydrogen from acetylene and then adds fresh hydrogen at the converter. Another process that operates at high severity is described in U.S. Patent App. Pub. No. 20090326288. In this process, the reference produces acetylene (up to 20 mol %) via methane pyrolysis and converts the reactor products (e.g., raw acetylene and hydrogen) to ethylene in a vapor phase wash coated hydrogenation reactor. The reference suggests that the selectivity to ethylene is maintained with a palladium titanate catalyst that has been additionally diluted with a solid dilutant and has been wash coated onto the walls of the reactor.
Although thermal pyrolysis reactors may be used to convert hydrocarbons into useful products, such as acetylene and ethylene, improved management of the hydrogen content is desired which can further enhance the processing of certain reactor products. Accordingly, it is desirable to provide a process that manages hydrogen in the conversion of hydrocarbon feeds into olefins in an enhanced manner.